Guard for grinding wheel



April 17, 1962 Filed April 15. 1959 M. M. BASS ET AL 3,029,563

GUARD FOR GRINDING WHEEL 6 Sheets-Sheet 1 BY if C. HAMMOND PHll/f I ROB/SCHUNG ATTORNEYS April 17, 1962 M. M. BASS ET A1.

GUARD FOR GRINDING WHEEL 6 Sheets-Sheet 2 Filed April 15, 1959 INVENToRs M/L'J' M @A55 BY ff C. HAMMOND PHP if: Ro/SCHUN@ ATTORNEYS 6 Sheets-Sheet 3 s N u w 0c 9 m NM 7 MJHMB ...A o Vn MA NMA o 1. HJ w 5 MY ArwP :s l m 4 ...n u l ,/.AHH h n MRL, -l W April 17, 1962 M, M. BASS ET AL GUARD FOR GRINDING WHEEL Filed April 13. 1959 /m @www ATTORNEYS April 17, 1962 M M, BAss ET AL 3,029,563

GUARD FOR GRINDING WHEEL Filed April 15, 1959 6 Sheets-Sheet 4 INVENTORAl MILLS M BASS HANS/'y M A'LL BY ff C. HAMMOND PHIL IP |71 ROB/SCHUNG ATTORNEYS April 17, 1962 M M BASS ETAL 3,029,563

GUARD FOR GRINDING WHEEL.

Filed April 13, 1959 6 Sheets-Sheet 5 INVENTORS Maf: M. am: RA/wsnr M. Btu By Ln c. HAMMOND ,vH/UP .7.' Ro/scHu/vs ATTORNEYS Aprll 17, 1962 M. M. BASS ET Al. 3,029,563

GUARD FOR GRINDING WHEEL Filed April 13, 1959 6 Sheets-Sheet 6 WMM www( w @Mb Hr rox/wxs' Unite This invention relates to a grinder and particularly to one in which the grinding wheel may be caused to oscillate at a controllable frequency and amplitude. This is a continuation-impart of our application Serial No. 574,- 72S, tiled March 29, 1956, now Patent No. 2,922,258, issued January 26, 1960.

In conventional tool grinding equipment, it is customary to provide a rotatable grinding wheel adjacent a worksupporting table. The table is normally movable for adjustment relative to the axis of the grinding wheel, so that the plane defined by the working surface of the wheel and the plane dened by the table top will intersect at whatever angle is desired to facilitate grinding the work in a desired manner. However, in all of these grinders, insofar as we are aware, it is necessary for the workman who is utilizing the machine, such as for grinding a tool point, to manually move the tool point across the working face of the grinding wheel. The reasons for such movement of the tool point across the face of the grinding wheel are well known to the industry and may be summarized here by pointing out that such movement of the tool tends both to speed the grinding operation and k'to work out any irregularities which may exist in the face of the grinding wheel, i.e., dress the wheel. This latter tends to secure a more nearly hat and a more smoothly ground surface than would be possible if no such movement of the tool point were employed. Further, this movement of the tool point etects a desirable amount of so-called cross-grain grinding and prevents the wheel grit from channeling thework.

However, where a workman is urging a tool toward an oscillating wheel by hand, it sometimes happens that the tool will slip past the edge of the wheel. When this happens, the too-l may jamb between the wheel and an adjacent portion of the table and, by stopping the machine practically instantaneously, cause severe mechanical damage thereto. Also, in electrochemical grinding with a diamond wheel, such entry of the tool between the edge of the wheel and the table will cause a short circuit which can cause severe damage to the wheel by knocking diamonds out of the wheel face edge. Further, if the workman is urging the tool against the wheel with an appreciable force, his hand may strike the wheel and be injured thereby.

A further problem arises when a wheel of this nature is arranged to be used with a portion of a table extending past a peripheral edge ofthe wheel in order that reversely bent, somewhat hook-shaped, tools can be ground. In this situation, the tool extends past and closely adjacent the periphery of the wheel so that a guard would prevent the use of the wheel for grinding such a tool. Therefore, it is necessary that the guard be arranged so that itcan be removed from its position along the peripheral edge of the wheel whenever necessary to enable the wheel to grind a hook-shaped tool.

Accordingly, a principal object of the invention has been the provision of a grinding machine effective for obtaining the individual shaping of the work, such as a tool point, which is customarily obtainable by hand guiding of said work with respect to the grinding surface, while eliminating the fatigue, inaccuracy and inconvenience of States Pater f: tc

manually moving the work back and forth across the face of the grinding wheel. 1

A further object of the invention has been to provide a machine, as aforesaid, in which the workman can hold the work, especially a tool point, stationary with respect to a supporting table, either with or without assistance of a mechanical holder or guide, and the relative motion of the work with respect to the axis of the grinding wheel is provided by the machine.

A further object of the invention has been to provide a machine, as aforesaid, having a device by which the axis of the grinding wheel is caused to oscillate with re spect to the work-supporting table.

A further object of the invention has been to provide a device, as aforesaid, including a guard extending around a substantial portion of said grinding wheel adjacent to its grinding face for preventing the tool, the operators hands, or the like, from accidentally slipping past the periphery of the wheel and being damaged or injured thereby. y

A further object of the invention has been to provide a device, as aforesaid, wherein said guard may be readily removed from its guarding position adjacent the periphery of the wheel when such a movement is required to enable the wheel to be used for grinding reversely bent, hook-shaped, tools.

A further object of the invention has been to provide a device, as aforesaid, in which such removal can be carried out quickly and easily and without actually removing the guard from the machine, whereby to keep .said guard n parent to persons acquainted with equipment of this general type upon reading the following disclosure and inspecting the accompanying drawings.

In the drawings:

FIGURE l is a side elevational view of the machine to which this invention relates, with the adjacent side sheets thereof broken away.

FIGURE 2 is a sectional View taken on the line 'II-II of FIGURE l.

FIGURE 3 is a sectional View taken on the line III-III of FIGURE 1.

FIGURE 4 is a sectional View taken on the line IV-IV of FIGURE 3. 4 l

FIGURE 5 is a sectional view taken on the line V- of FIGURE l.

FIGURE 6 is a sectional view taken on the line VI-VI of FIGURE 3.

FGURE 7 is a view of a modification taken with the guard mechanism removed from the machine and viewedv from the front ofthe machine.

FIGURE 8 is a side view of the guard shown in FIG- URE 7.

FIGURE 9 is a top view of the guard shown in FIG- URE 7.

FIGURE l0 is an oblique view of a machine showing the guard of FIGURE 7 in position thereon, one portion of said guard being in operative position and the other portion being out of operative position.

For the purpose of convenience in description, the terms upper, lower, left, righ and derivatives thereof, will have reference to the machine and parts thereof as appearing in FIGURE 2. n The terms front and rear will have reference to the left and right sides, respectively, of the machine as appearing in FIGURE l. The terms innen outer, and derivatives thereof, will have reference to the geometric center of said machine and, parts thereof.

3 GENERAL DESCRIPTION In meeting the objects and purposes above set forth, we have provided -a machine having an adjustable, but relatively stationary, table with which a manually operable tool holder may be used, if desired, said machine having a structure for supporting a rotatable grinding wheel adjacent to said table. The grinding wheel is mounted for oscillatory movement transversely of its rotational axis. During such movement, the center of said wheel traces an arcuate path which is generally parallel to the surface of the grinding table, that is, the tangent at the midpoint of said path is parallel both to the surface, and to an adjacent edge 50, of said table. This result is obtained by securing the grinding wheel 11 (FIGURES l and 4) to a shaft 12, which is rotatably mounted adjacent to the table 14 upon a shaft support bracket 13. The support bracket 13 is in turn pivotally supported by the bearing assembly 20 upon the platform 15 of the machine frame 10. The shaft 12 is continuously rotated by a belt 16 driven by the motor 17.

Oscillation of the bracket 13 about its pivotal support 20 is, in the preferred embodiment here shown, effected by a lever 18 (FIGURES 2 and 5) pivotally supported by the pillow block 19 on the upper wall 34 of frame 10 and connected to the bracket 13 by the pitman 21. The lower end of the lever 18 is caused to oscillate, or is alternatively held against oscillation, by a roller 22, which is mounted upon the shaft 26, rotatable at a controllable speed with the pulley 25. The shaft 26 may be moved radially of the axis of the pulley 25 by a hand wheel 23 working through a mechanism 24 for adjusting the amount of eccentricity of the shaft 26 with respect to said pulley. The amplitude of oscillation of said wheel 11 is, therefore, controlled by the eccentricity, if any, of the roller 22 with respect to said pulley 25. Rotation of said pulley 25 is secured through the belt 27 driven through a suitable speed reducer 28 from, and by, the motor 29. The speed of such oscillation is adjusted through the speed reducer 28 in response to adjustment of the hand wheel 31.

The table is arranged in somewhat U-shaped form in front of and extending on both sides of the wheel with the portions which extend past said wheel arranged for movement toward and away therefrom in the plane of oscillation of the wheel in order to adjust same appropriately to the amplitude of oscillations of said wheel.

The guard structure is mounted on the housing irnmediately behind said wheel and supports a pair of arcuate segments spaced. from but closely adjacent the peripheral edge of the wheel. Said segments are of sufficient length to extend around said wheel to a point below said table. The guard is then rendered removable either by rotating the entire mounting unit around the axis of the wheel or by removing one fastening for a guard segment and thereby rotating it around another fastening into a non-interfering position.

DETAILED CONSTRUCTION A. Frame and Table As shown particularly in FIGURES l and 2, the base frame of the grinding machine to which this invention relates is upright, substantially rectangular, in this particular embodiment, and fabricated from any sturdy, conventional material, such as steel plates. A platform or bed plate is mounted upon the upper wall 34 of the frame 10 and extends forwardly of the front wall 123 of the machine frame 1). The forward end of the platform 15 is provided with ways 35 on its upper surface, which engage and slidably support the base 36 of the table 14 for slidable, adjustable movement rearwardly and forwardly of the machine frame 10. Such movement is obtained by means of the threaded engagement between the screw 37 (FIGURES 3 and 4) and the double or split nut 38, which has front and rear portions 40 and 41,

respectively, through both of which the screw 37 is threadedly received. One portion, here the rear portion 41, is rigidly secured to the platform 15 between the ways 35. The screw 37 is rotatably supported upon the front end of the table base 36 rand heldv against axial movement with respect thereto in a substantially conventional manner. A hand wheel 45 is secured to the front end of the screw 37 for effecting rotation thereof, hence movement of the base 36 along the ways 35.

The table base 36 (FIGURES 3 and 4) extends laterally of, and above, the ways 35 and supports the bottom of a hood 46, which substantially surrounds the table 14 and the grinding Wheel 11. Left and right table support members 47 and 48 (FIGURES l and 4) are mounted upon, and extend upwardly from, the table base 36 adjacent to its lateral edges (FIGURE 3) within the hood i 46. The members 47 and 4S are preferably hollow and have concave, arcuate upper surfaces 49 having a substantially horizontal common axis 50 (FIGURE 4) lying within the plane defined by the upper surface 51 of the table 14. A pair of table brackets 52 and 53 (FIGURE 5) are secured to, and depend from, the lower surface of the table 14 near its lateral edges. Said brackets 52 and 53 have arcuate, convex lower surfaces 54 (FIGURE 4), which are snugly, slidably and respectively receivable into the upper, concave surfaces 49. Side plates 55 are secured to, and extend downwardly beyond, the lateral sides of the brackets 52 and 53. Said side plates 55 embrace the lateral sides of the support members 47 and 48 when they are engaged by the brackets 52 and 53, respectively, in order to prevent dirt from entering between the brackets and their corresponding support members. The brackets 52 and 53 are slidable with respect to the support members 47 and 48 for effecting tilting of the table 14 about the axis 50. The table 14 may include a plurality of removable and replaceable wear plates 77 (FIGURE 6) and a recess 78 (FIGURE 5) in its rearward edge, into which the grinding wheel 11 is received. The portion of the table 14 on opposite lateral sides of said recess 78 are provided with wear plates 79 and 89, which are movable toward and away from each other to vary the lateral extent of the recess 78 for reasons appearing hereinafter,

B. Grinding Wheel and Wheel Support The bearing assembly 20, which pivotally supports the support bracket 13 (FIGURES l and 4) includes a pivot shaft 82, which is substantially parallel with the extended axis of the screw 37, and is secured at its opposite ends in the blocks 83 and S4 (FIGURE l) mounted upon the rearward end of the platform 15. The shaft 82 is preferably located substantially directly behind the centerline of the table base 36. The support bracket 13 (FIGURE 4) includes a cylindrical housing 85 at its lower end, which encircles the pivot shaft 82 and is rotatably mounted upon said shaft by means of the bearings 86. Said bracket 13 also includes a support plate 87, which is secured to, and spaced from, the housing 85 by a pair of Webs 88. The shaft housing 89, in which the grinder shaft 12 is rotatably supported by means of the bearings 91, is mounted upon the plate 87. The grinder shaft 12 is axially parallel with the pivot shaft 82 and extends both forwardly and rearwardly from within the shaft housing 89.

A grinding wheel mount 92 (FIGURE 4) is rigidly secured to the front extensions 93 of the shaft 12 by means of a bolt 94 in a substantially conventional manner. The rearward face of the wheel mount 92 and the forward, annular end wall 95 of the shaft housing 89 `are provided with a suitable sealing device for preventing the waste materials of the grinding operation from getting into the bearings 91. The grinding wheel 11 is secured to the front surface of the wheel mount 92, as by means of bolts 36 (FIGURE 4), so that the planar grinding face of said wheel 11 lies in a substantially vertical plane,

and said wheel can be disposed adjacent to, and parallel with, the edge 78a (FIGURE 4) of the table 14 within the recess 7S.

C. Wheel Guard and Table Extensions A sleeve 1G11 (FIGURE 4) is adjustably supported upon the forward end of the shaft housing 89 for controlled movement about the shaft 12 in both rotational directions. A detent mechanism 1111 tends to hold the sleeve 1110 in selected positions with respect -to the shaft housing 89. Said sleeve 1011 is Idisposed within the hood 46 and supports a forwardly extending, arcuate flange 1112, upon which the arcuate guard element 1113 is secured. In this particular embodiment, the tilting axis t) of the table 14 is disposed somewhat below the axis of the grinding shaft 12. However, the opposite ends of the arcuate guard 103 `are capable of extending simultaneously below said table upper sur-face 51 in one selected position of said guard, effected by appropriate positioning of the sleeve 101B upon the shaft housing 39. The guard 1113 is spaced slightly radially outwardly of the grinding wheel 1v1, and the front surface of `said arcuate guard 103 is preferably substantially co-planar with the front, or grinding, surface 104 of the wheel 11. Said sleeve 100 also has an annular llange 911 (FIGURES 4 and 6), pref erably near its forward edge, which extends radially beyond the periphery of the grinding wheel 11. The flange 90 prevents the wheel 11 from striking those portions of the table 14 on opposite sides of the recess 78 when said wheel 11 is oscillated and the guard 103 is removed from, or rte-positioned on, the housing 89. As shown in FIGURES 3, 5 and 6, the end wear plates 79 and Si), which are disposed on the table 14 radially outwardly from the grinding wheel 11, yare in their normal, or extended, position when the arcuate guard 103' is centered. However, when said guard 163 is moved, for purposes appearing hereinafter, to its broken line position 1035i, as shown in FIGURE 5, the end plate 79 adjacent to that end of the guard 103 which is raised above the level of the table may be moved in adjacent to the peripheral edge of the grinding wheel 11, as indicated at 79u, or as close `as the ange 90 on the sleeve 1li()l will permit.

Means, including the tube 195, is supported by the flange 1&2 for directing cooling and/ or grinding lluid at the center of the wheel 11.

he support bracket 13 and the portion of the shaft 12 and the shaft housing 89 disposed outside of the hood 46 are substantially enclosed hy an enclosure 97 (FIGURE 4), which is mounted upon the frame lll and has an opening 98' in its front wall, through which said shaft housing S9 extends. The opening 9S is laterally elongated to permit oscillation of said housing S9 with respect to the enclosure 97. The space between the housing S9 and the enclosure 97 is closed by an annular sheet 99 having a flanged, internal edge 99a, which snugly em braces the housing 89. Said ilanged edge 99a, hence the sheet 99, is secured to the housing 89 by a resilient ring 81 and said sheet 99 slidaoly and snugly engages the front wall of the enclosure 97 'to provide a dust seal.

D. Wheel Drive Mechanism The rear extension 106 of the shaft 12 supports a pulley 107 (FIGURES l Iand 4)., which is connected to a pulley 1118 by the belt '16, said pulley 16S being mounted upon the shaft ofthe motor 17. The motor 17 is supported below the platform 15, in this particular embodiment, upon a motor mount 169 so that the axis of said motor is parallel with lthe shaft 12 (FIGURE 2). The motor mount 169 is pivotally supported along one edge thereof, parallel with said motor axis, upon a pivot shaft 111, which is supported upon the frame 10. An arm 112 extends from the opposite edge of said motor mount 169 `and supports a substantially horizontal pin 113 near `its free end, which pin slidably extends through a lengthd wise slot 114 in the support Ibar 115 near the lower end thereof. The upper end of said bar 115 (FIGURES 1 and 2) is pivotally mounted upon the upper wall 34 of the machine frame 10.

E. Oscillatory Drive Mechanism The pitrnan 21 is pivotally supported at one end upon the front web 38 between the support plate 87 and the cylindrical housing 85. The other end of said pitman 2,1 is pivotally secured to the upper end of the lever 13, which lever is pivotally supported between itsupper and lower ends by a pivot shaft 116 land a pillow block 19 mounted upon the top wall 34 adjacent to the bearing assembly 20. The lower end of the lever 1S is provided with a slot 118 which is elongated lengthwise of lsaid lever 18. The roller Z2 (FIGURES 2 and 5) is rotatably disposed within the slot 118 and is engageable with the side walls of said slot. The shaft 26 is secured to the adjustment mechanism 24 for effecting movement of the roller 22 into and out of a position of concentricity with the pulley 25.

The pulley 25 is connected by the belt 27, in a su-bstantially conventional manner, to the output of the speed `reducer 28, which is controlled by the hand wheel 31 mounted thereon, and which is connected to the motor 29, also in a substantially conventional manner.

A pump 136 (FIGURE 2) may tbe provided for forcing a coolant or lubricant through the tube l105 Iand returning said iluid to the pump from its point of collection in the hood 46 -by conventional means, not shown.

OPERATION After the grinding wheel 11 (FIGURE 4) is secured in place with respect to the shaft or spindle 12, the table 14 is then moved rearwardly until the rearward edge 78a (FGURES 4 and 6) of said table 14 Within the recess 7S `and between the end wear plates 79 and 80 (FIGURE 5) is spaced a relatively slight `distance from the front face 104 of the grinding :wheel 11. Where the tool, such as that indicatedl in broken lines at 137 in FIGURE 4, is of the type which may be supported upon the wear plates 77 in front of the grinding wheel 11, the horseshoeshaped guard 103 (FIGURES 3 and 5), which encircles the exposed portions of `the peripheryl of the grinding wheel 11, will be :disposed so that its opposite ends are below the surface of the table 14, as shown in FIGURE 5. In such case, the end wear plates 79 and SG (FIGURES 3 and 6) will be moved laterally outwardly of the edges of the other wear plates 77. However, if it becomes desirable to work on a hook-type tool of the type shown in broken lines at 13S in FIGURE 6, then the guard 103 may be rotated in one direction or'the other around the axis of the shaft 12 into a position to expose the periphery of the wheel 11, las indioated'in broken lines at 103e in FIGURE 5. The end wear plate 79l adjacent to the exposed portion of said wheel is then moved into a position, as shown in broken lines `at 79a in FIGURE 6, so that v it can hold the tool 138, which must extend partially behind the plane dened by the grinding face 104.

When the proper adjustment of the table has been obtained, the motor 17 (FIGURE l) can then be energized, thereby causing the shaft 12 land grinding wheel 11 to rotate. The motor 29 is also energized, which drives the speed reducer 28, which in turn rotates the pulley 25 of the adjustment mechanism 24.

The pulley 25 acts through suitable means within the housing 122 to drive the crank 26 and thereby eifect an y oscillatory pivoting of the lever 18 about the pivotal axis provided by the lever bearing 19. Such reciprooation will be transmitted by the pitman 21 (FIGURE 2) to the support bracket 13 for effecting 1a corresponding pivotal reciprocation of said support bracket about the pivotal axis thereof provided by the Abearing yassembly 20. This will cause the shaft 12 to oscillate through a relatively small arc crosswise of the machine, the tangent of said arc at its midpoint being substantially parallel to the pivot axis 50 of the table 14, `and thereby effect a similar lateral oscillation of the grinding wheel 11. Where the grinding wheel, as shown here, has a relatively narrow grinding face 104, the oscillation of the grinding wheel will be relatively small and, as `a general rule, will be somewhat less than the radial width of the grinding face on said wheel 11. Thus, the path traversed by the axis of the shaft 12 during said oscillations, although arcuate, will be relatively flat and substantially parallel to pivot axis t) of the table 14. However, since the path of oscillation of said shaft 12 is arcuate, and since the radius of this arc is substantially less than, here approximately one-half of, the axial distance between the shaft 12 and the shaft of the driving motor 17, some provision must be made for keeping the belt 16 under uniform tension during the operation. This is accomplished by pivotally supporting the motor mount 16'9 upon the pivot shaft 111 so that said motor partially hangs upon the belt 16. Thus, as the shaft 12 moves upwardly and downwardly a relatively small distance during the arcuate movement thereof, the motor 17 is free to move upwardly and downwardly this same slight distance.

The flexible and resilient `annular sealing sheet 99 (FIG- URE 4) permits movement of the shaft housing 89 with respect to the enclosure 97 during the oscillation of said shaft housing 89 without impairing the seal provided thereby. The opening 98 in the enclosure 97, through which the shaft housing 89 extends, is suliiciently large to permit the desired oscillation of the shaft housing S9.

Adjustment of the oscillation distance or amplitude of the shaft 12 is effected by turning the hand wheel 23 as- Sociated with the adjustment mechanism 24. By appropriate adjustment of the hand wheel 23, the roller 22 can be caused to be completely concentric with the pulley 25, whereby the grinding wheel 11 can be caused to rotate without any reciprocation or oscillation whatsoever.

It will be recognized that the adjustment of the table 14, the guard 103, the end wear plates 79 and S0, the adjustment mechanism 24 and the speed reducer 28 can be effected while the machine is in operation.

The necessary adjustments having thus been completed, the tool, either as shown at 137 in FIGURE 4 or at 138 in FIGURE 6, is placed upon the table 14 and held there, either manually or by mechanical means, while the grinding wheel 11 and the guard 103 reciprocatcs with respect to the table 14, as indicated by the solid line and broken line positions of these parts in FIGURE 6. The grinding wheel 11 is protected from striking those edges of the table 14 which define the lateral ends of the recess 78 by the flange 9) on the sleeve 100, which iiange eX- tends radially beyond the periphery of the wheel 11. The guard 103 provides additional protection, both for the wheel 11 and the hands of the workman, by closely surrounding the portion of the wheel 11 exposed above the table 14.

MODIFICATION Referring now to FIGURES 7 to 10, inclusive, there is shown a modification which is somewhat more adaptable to use with electrolytic types of grinding operations than is the form shown in FIGURES l to 6, inclusive, in that it eliminates the necessity for the housing G to rotate on and with respect to the shaft housing 89. It has been found that in electrolytic types of grinding, the salts used in the electrolytic liquid often enter into the space between the housing 100 and the housing 89, deposit therein and render such movement extremely dicult and often impossible.

In the structure shown in FIGURES 7 to l0, inclusive, there is provided a housing 201 generally similar to the housing 160, previously described, but provided with flanges 20.?. and 2553 which vare bolted together by which said housing 201 is fastened rigidly to the shaft housing 89. Supported on and by the housing 201 is an upwardly and forwardly extending portion 204 whose forward face 205 is parallel with, and substantially coplanar with, the plane of the cutting surface of the wheel and is located closely above said wheel, the position of said wheel with respect to the guard being indicated by the broken line W. Said housing 201 has a central portion 206 on which is mounted, if desired, a center guard 2G5a for said wheel by which the central portion of the wheel is filled when a cup-type wheel is utilized. Such a center guard is further described in U.S. Patent No. 2,361,550.

Extending sidewardly in `both circumferential directions frorn the central portion 206 (FIGURE 9) of the guard structure and off-set slightly backwardly from a condition of co-planarity with the forward or cutting face of the wheel are a pair of guard supporting wings 207 and 208. Each of these wings is provided with at least two threaded openings of which the openings on wing 207 are shown at 299 and 211 whose purposes will be further indicated below.

A pair of guard members 214 and 216, preferably of non-electrically conductive material where the machine is to be used for electrolytic grinding, comprise a pair of arcuate segments which are each axed, respectively, to said wings 207 and 203. Suitable openings are provided through each of said guard members in register with the threaded openings above mentioned. Suitable threaded fastening means, as the screws 217, 218, 219 and 221 are provided for cooperation with said threaded openings for holding said guards 216 and 214 tightly against said wings. Said guards are each shaped so that they are positioned closely adjacent the peripheral surface of said wheel and so that their respective front faces 222 and 223 are co-planar with the front face of said wheel. The guards are of such length that they extend slightly below the surface of the table, the same being indicated with respect to guard structure shown in FIGURE 7 by the broken line 224 and shown in FIGURE l0 at 14.

Where a tool having its point on the end thereof is to be ground by the apparatus herein described, the guard will be lowered into the position shown in FIGURE 7, and the tool applied against the face of the wheel in a conventional manner, the guards 214 and 216 preventing the ltool from slipping past the periphery of the wheel if the workman has not properly allowed for reciprocation of the wheel in his locating of the tool. If, however, a reversely cut, or hook-shaped, tool is to be ground then the screw 217 or the screw 221, depending upon which side of the grinding wheel is to be used, will be removed and the guard 214 or guard 216 associated therewith turned upwardly in a position as shown by guard 214 in FIGURE 10. In this situation, the reciprocation of the wheel will normally be stopped, or at least held to a very small magnitude, and the tool will be supported on and by an appropriate one of the wings 79 and 80 in the manner shown in FIGURE 6. The grinding will then proceed as desired.

When the grinding of the hook-shaped tools is completed the guard 214 or 216, which ever one is raised, can then be readily returned to the normal position as shown in FIGURE 7 and the screw 217' or 221, which ever one was removed, restored into position for holding its associated guard in position.

Although particular, preferred embodiments of the invention have been disclosed hereinabove `for illustrative purposes, it will be understood that variations or modifications thereof, which do not depart from the scope of such disclosure, are fully contemplated unless specifically stated to the contrary in the appended claims.

What is claimed is:

l. In an oscillating type grinding machine including a grinding wheel, a shaft for supporting and rotating said grinding wheel and a housing surrounding said shaft, means supporting said shaft for both rotary and oscillatory movement; and a table having a generally L- shaped portion arranged across the cutting face of said grinding wheel and extending past at least one peripheral edge thereof, the improvement comprising: guard structure for said wheel mounted on said housing and having a central portion extending therefrom to a position substantially above the centrer of said wheel, said central portion including a pair of laterally extending wings extending in opposite circumferential directions with respect to said wheel; a pair of arcuate segments mounted respectively on said wings and having `their forward faces arranged coplanar with the forward face of said wheel, each Segment extending circumferentially at least part way around said wheel to a point below the upper surface of said table, said segments being pivotally related to said wings for pivotal movement with respect thereto away from close proximity to said wheel; and detachable means for holding said segments rigidly with respect to said wings and against pivotal movement with respect thereto.

2. The device defined in claim 1 wherein said housing has a cylindrical portion and said guard structure is provided with portions tdening a split sleeve for arrangement around the cylindrical portion of said housing and including means rigidly fastening the portions of said sleeve together and removable with respect to said housing.

3. Guard structure for a face type grinding wheel wherein said wheel is arranged for back-and-for-th movement with respect to a work-supporting table and the means for supporting and driving said wheel includes a housing which moves back and forth in synchronism with the back-and-forth movement of said wheel, comprising in combination: means rigidly engageable with said housing and having a central portion extending upwardly and forwardly to a point above and substantially centered over said wheel; at least one wing extending sidewardly from said central portion and extending in a generally circumferential direction around said wheel; an arcuate segment pivotally affixed adjacent one of its ends to said `wing for pivotal movement, the other end of said segment being unsupported and being free to move toward and away from the periphery of said wheel whereby said segment can be moved between a normal position wherein its radially inner edge is substantially concentric with the radially outer edge of said wheel and positioned in close proximity thereto to a position where the other end of said segment is spaced a substantial distance from said wheel, and means for removably holding said segment in said normal position.

4. A guard structure for a face-type grinding wheel comprising center support means adjacent said grinding wheel and stationarily mounted with respect to the axis of rotation thereof; a pair of arcuate segments movably mounted on said center support means and extending in opposite directions therefrom, said segments being substantially coplanar with the face of said grinding wheel and being independently movable between normal positions wherein their radially inner edges are close to the periphery of said grinding wheel and positions where same are substantially spaced from the periphery of said grinding wheel; and removable fastening means extending through said segments close to the adjacent ends thereof and' into said center support means for removably holding said segments in their normal positions.

5. A grinding machine, comprising a face-type, rotatable grinding wheel; a work-supporting table; means supporting said grinding wheel for back-and-forth movement with respect to said work-supporting table; a housing secured in fixed position with respect to the axis of rotation of the grinding wheel, said housing having a central portion positioned above said wheel; said housing having a pair of wings extending in opposite directions therefrom and partially surrounding portions of the periphery of said grinding wheel; a pair of arcuate guard segments pivotally mounted at one end thereof on said wings for independent pivotal movement between a normal position where their radially inner edges are close to the periphery of said grinding wheel and a position where same are substantially spaced from rthe periphery of said grinding wheel, said segments being of suiicient length that they extend below the upper surface of the work-supporting table when in their normal positions, said segments having their forward faces substantially coplanar with the forward face of said grinding wheel; and detachable means extending through said segments adjacent said one end thereof and into said Wings forv holding said segments in their normal position, the remainder of said segments being unsupported so that same may 'be pivoted to a position wherein they are located Va substantial distance above said table.

6. A guard structure according to claim 5 wherein said segments are of electrically nonconductive material.

7. A grinding machine including a face-type grinding wheel, a shaft for supporting and rotating said grinding wheel and a housing surrounding said shaft, means supporting said shaft for rotation and for back and forth movement rtransverse to the axis thereof; a table positioned in front of the face of said grinding wheel and having an extension opposed to and spaced from the periphery of said grinding wheel; a support extending over said grinding wheel; an arcuate segment mounted on said support and means pivotally mounting one end of said segment on said support so that said segment can 'be moved between a iirst position wherein it extends around a portion of the periphery of said grinding wheel and into the space between said extension and the periphery of the grinding wheel and a position where said segment is substantially spaced from the periphery of said grinding wheel, the other end of said segment being unsupported and free to move in response to pivoting thereof with respect'to said support; and releasable means for normally holding said segment in said rst position.

References Cited in the tile of this patent UNITED STATES PATENTS 

